Serotype variability, genomic plasticity and increasing antibiotic resistance of S. pneumoniae, pose considerable challenges for designing intervention strategies for this global public health concern. There is a need for the identification as well as characterization of novel vaccine candidates for effective immunization against pneumococcus, as the available vaccines are not effective against all serotypes. Polyamines are ubiquitous small cationic molecules necessary for pneumococcal growth and virulence. Therefore, intracellular polyamine levels are tightly regulated, thus making polyamine transport mechanisms a highly attractive focus for investigation on pathogenesis and immune responses. Our preliminary results indicate that impaired polyamine transport causes attenuation of pneumonia in mouse models. However, the pathogen-host interactions responsible for this attenuation are yet to be characterized. Our central hypothesis is that attenuation in pneumococcal pneumonia by impaired pneumococcal polyamine transport is due to the reduced virulence factor gene expression and/or reduced resistance to host innate immune responses. We will test this hypothesis by conducting the following specific aims. Specific aims: 1-identify polyamine responsive pneumococcal genes and pathways by comparing gene expression of wild type and ApotABCD S. pneumoniae (a strain with genetic deletion of polyamine transport operon) in a mouse model of pneumonia ; 2-determine the host innate immune responses to polyamine deficient pneumococcus by measuring the expression of antimicrobial proteins, acute phase proteins, opsonophagocytosis by macrophages and neutrophils, and host signaling pathways and functions including Toll-like receptor signaling, using proteomics. Successful completion ofthe proposed studies will identify the pneumococcal molecular mechanisms responsive to polyamine transport as well as specific host innate immune responses. Project results will shed light on the role of polyamines in infectious diseases in general for the identification of unique intra and extracellular targets for design of novel vaccines or therapeutics in future.